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Avonex (interferon beta 1a)

Other names: Interferon beta 1a

Avonex is a disease modifying drug for relapsing remitting MS.

You self-inject Avonex into a muscle once a week to reduce the number and severity of relapses. It reduces the number of relapses by about one third (30%), compared to taking placebo.

Common side effects include flu-like symptoms and injection site reactions.

What is Avonex used for in MS?

Avonex is a disease modifying drug (DMD) for relapsing remitting MS. You have fewer relapses than you might have had with no treatment and any relapses you do have should be less severe. It can also be used after a first episode of neurological symptoms (clinically isolated syndrome) to delay conversion to multiple sclerosis.

Avonex is a moderately effective (category 1.1) DMD; in clinical trials people taking Avonex had about 30% fewer relapses than people taking placebo. In clinical trials, MRI scans showed people taking Avonex had fewer, smaller or no new areas of active MS (lesions). Avonex may also slow down the build-up of disability associated with MS.

Who can take Avonex?

Avonex can be prescribed for adults with active relapsing remitting MS.

Avonex can also be prescribed for people who have had a first episode of neurological symptoms (clinically isolated syndrome) and have a high risk of developing MS.

Avonex has been approved for use on the NHS since 2002 under the Department of Health's Risk-sharing Scheme. It can only be prescribed by a neurologist.


It's important that you tell your MS team if you have any health problems or are taking other medicines. Avonex may not be suitable if you have severe depression or suicidal thoughts.

Conception and pregnancy

Pregnancy is not recommended during treatment.

If you are trying for a family, talk to your MS nurse or neurologist about whether you should continue to take Avonex until you are pregnant.

If you become pregnant while on Avonex, your neurologist or MS nurse may recommend you stop taking it.

How do I take Avonex?

You self-inject Avonex into a muscle once a week. Avonex is supplied in several different formats; your MS nurse can explain the different injectino devices and help you choose the most appropriate one for you.

Your MS nurse will show you how to do the injections, discuss the practicalities and offer advice or training and ongoing support if you should need it.

To give your body a chance to get used to Avonex and reduce the impact of side effects, your doctor or MS nurse may suggest you start on a lower dose (dependent on injection device).

What side effects could I get with Avonex?

Common side effects include:

  • Flu-like symptoms, such as headache, muscle ache and stiffness, chills or fever, following an injection
  • Injection site reactions

You are more likely to have these side effects when you first start taking Avonex. Most people have mild to moderate side effects which tend to go away over time.

A neurologist or MS nurse may suggest ways to reduce these side effects including:

  • To help with flu-like symptoms, it may be helpful to change the time of day of injection in order to sleep through the worst of the side effects
  • To help reduce fever, paracetamol or ibuprofen can be taken before the injection and at four to six hour intervals after the injection, as required

Common side effects (affecting more than 1 person in 100)

  • flu-like symptoms
  • headache
  • injection site reactions
  • blood cell abnormalities
  • feeling weak or tired
  • difficulty sleeping
  • diarrhoea, nausea and vomiting
  • muscular or joint pain
  • infections
  • depression

Less common side effects (affecting less than 1 person in 100)

  • changes in menstruation (periods)
  • liver abnormalities
  • allergic reactions
  • heart problems and hypertension
  • hair thinning or loss
  • damage to small blood vessels leading to kidney problems

A full list of side effects is included in the manufacturer's Patient Information Leaflet.

Assessment before treatment

Before starting Avonex, you should have blood tests to measure blood cell counts and check liver function.

Assessment during treatment

Once you've started treatment, you'll have blood tests to measure blood cell counts and monitor liver function, generally every three months for the first year, then less frequently. Depending on local practice, the tests may be carried out at a local GP surgery or it may be necessary to attend a hospital clinic.

How does Avonex work?

Interferons are proteins that occur naturally in the immune system. It is thought that beta interferon acts by reducing both inflammation and the immune response that is attacking the body's own myelin.

Avonex research

What are the results so far?

Avonex has been studied extensively since the early 1990s. The following study first demonstrated the effectiveness of Avonex:

  • MSCRG Study: Multiple Sclerosis Collaborative Research Group Study - Avonex compared to placebo

In this clinical trial, 301 people with relapsing remitting MS took either Avonex or placebo for 2 years. The main measure of the study was the time it took for participants to have an increase in disability of 1 point on the EDSS scale which lasted for at least 6 months. The group taking Avonex were significantly less likely to have this increase in disability. At the end of 2 years it was estimated that approximately 35% of those taking placebo and 22% of those taking Avonex had increased disability, a 37% reduction compared to placebo. Avonex reduced the relapse rate by 32% compared to placebo and also reduced the number of brain lesions on MRI.

Last updated: November 2017
Last reviewed: September 2015
This page will be reviewed within three years